Wave guide switch



March 8, 1955 P. v. DE LA COVA ETAI- WAVE GUIDE SWITCH 2 Sheets-Sheet 1 Filed April 23. 1951 Paul V. de lo Covu John J Walls INVENTORS.

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March 8, 1955 I v, DE LA cov ET AL WAVE GUIDE SWITCH I 2 Sheets-Sheet 2 Filed April 23, 1951 7 Paul V. de lo C600 John .1. Walls INVENTOR-Sl United States Patent WAVE GUIDE swrrcn Paul V. de la Cova and John J. Walls, Towson, Md., as-

signors to Bendix Aviation Corporation, Towson, Md., a corporation of Delaware Application April 23, 1951, Serial No. 222,506

8 Claims. (Cl. 333-7) This invention relates generally to the control of electromagnetic energy and more particularly to a method of and means for switching guided electromagnetic energy.

In prior art switches for guided wave energy, it has been well known to provide a conducting plate which is movable to a position across the cross-sectional area of the waveguide to effectively short circuit the guide path and provide a barrier beyond which no wave energy flows. Such a plate need not be in physical contact with the waveguide periphery but may be spaced at an appropriate distance to permit mechanical clearance and still provide an effective short circuit to the high frequency energy for which such devices are used.

The difficulty encountered upon the operation of such devices in the past has been due to the fact that as soon as the barrier plate entered the cross-sectional area of the guide large amounts of energy were reflected therefrom resulting in a large standing wave ratio (SWR). In a particular application of this type of switching in which two antennas are required to be alternately energized from a common source, the waveguides connecting the separate antennas to a common source are alternately traversed by a barrier plate switch. However, no relative orientation of the barrier terminating boundaries of the plate in such a device will prevent reflections and large SWR during the switching interval. The impedance mismatch resulting in this high SWR causes all the difficulties associated with a large SWR, such, for example, as frequency shift and the limitation of useful power output.

In a system in which a magnetron oscillator is switched between alternate loads, the frequency disturbances associated with switching have been so extreme that automatic frequency control (AFC) of the associated receiver circuits has heretofore, been impractical. This problem has been so severe that in recent years the design of systems utilizing dual antennas such, for example, as the ground controlled approach (GCA) landing system, separate transmitter, receiver and AFC systems have been providedfor each antenna.

An object of this invention is to provide a new and improved method and apparatus for switching energy in a waveguide.

Another object of this invention is to provide an improved method of waveguide switching in which the area of interruption of energy propagation changes during the switching interval progressively in accordance with the strength of the electric field distribution.

A further object of this invention is the reduction of reflection effects in waveguide switching through the use of contoured edges on switch elements.

Another object is to provide smooth energy transfer in alternate load switching without any appreciable standing wave ratio transient disturbance by means of reciprocal contoured switching plates.

A further object is to provide, in an alternate branch waveguide transfer system, a switching method and apparatus having contoured barrier plates movable in such a manneras to maintain the sum of the effective transmission areas in the branch waveguides substantially constant.

A further object of this invention is to provide a constant load transfer switch for a rectangular waveguide system in which barrier plates having a sinusoidal notch contoured therein traverse the active branches of the transfer system in such a manner that the sums of the open areas of these branches remains substantially constant.

The present invention, in accordance with the preferred embodiment thereof, provides a conductive barrier element movable into wave energy short circuiting position transverse to the waveguide and having a contoured edge such that a barrier terminating boundary progresses across the area of the guide from regions of low electric field intensity to regions of high electric field intensity. When the present invention is utilized to transfer a connection between two or more guides a reciprocal function is carried out by a similarly contoured element as it moves to open another guide path and the relative spacing of the opening and closing elements is such that the sums of the effective transmission areas in the active guide paths remains substantially constant at an optimum value.

In a device of the latter type designed for use in a GCA system the maximum voltage SWR (VSWR) encountered.

at any instant during the switching interval was 1.12 as compared with a maximum VSWR of 3.8 during switching which was representative of the best VSWR obtainable with prior art devices.

The invention will be described with reference to a rectangular guide excited in the TE1,'o mode, except where Fig. 2 is a view showing, by successive elevation illus-v trations of a fragment of the switch, progressive positions of the contoured elements as switching occurs in a device similar to Fig. 1;

Fig. 3 shows the relation between various contours and a waveguide cross-section;

Fig. 4 is a perspective view showing a modification of the invention in a switching operation;

Fig. 5 is an elevational view illustrating the application V of the invention to a single switching operation;

Fig. 6 is a fragmentary elevational view of the device of Fig. 5 a short time interval later; and

Fig. 7 is a fragmentary elevational view illustrating the application of the principle of the invention to higher order modes of electromagnetic energy.

Referring now to Fig. 1, there is shown a T junction.

generally designated 11 and having a common guide path 12 and two branch guides 13 and 14. Narrow openings 15 and 16 exist in the boundaries of branch guides 13 and 14, respectively, and are preferably spaced an even multiple quarter-wavelength electrical distance from the series. type junction of T 11. For shunt type T junctions odd.

multiple quarter-wavelength spacing is preferred, as will be understood by those skilled in the art. The branch guides continue beyond the openings at 13 and 14' to a desired antenna or other termination, not shown.-

Mounted for rotation adjacent the guide are two rotors 17 and 18, each having a portion of major radius R which is substantially semi-circular in shape and which passes through respective openings 15 and 16 during rotation. The rotors 17 and 18 are fixed relative to each other during rotation in such a manner that at any given time the portion of major radius R of only one rotor is effective to block the transmission path in the branch guide through which it moves, except during the transition period as will be more fully described hereinafter. This motion of the rotors 17 and 18 therefore provides the connection of common guide 12 alternately between branch guides 13' and.14' with switching occurring once.

for each half-cycle of rotation of the rotors.

The effective barrier edges of the rotors 17 and 18 are formed by the respective portions designated 21, 21' and 22, 22'. These edges, in accordance with the teaching of this invention, are contoured and moved across the guide in such a manner that the waveguide is closed off thereby progressively from regions of low electric field intensity to regions of high electric field intensity and conversely the guide is opened progressively from regions of high to I Patented Mar. 8, 1955 9 ss c field n s tr, c ion s acccmn ish in the embodiment of Fig. 1 by making the radius R large so that the motion of edges 21, 21 and 22, 22' is substantially translational across the guide face and by contouri'ng approxlmately sinusoidal half-cycle notches 23, 23, and 24, 24' in the edges, These notches are centered with respect to the. broad; dimension of the guide when positioned to move across the guide face. This combination'of' contour and motion will satisfy the aforesaid requirements of a progressively controlled barrier terminating boundary for a rectangular guide excited in the T151 mode, the electric field of which is represented symbolically by the arrows 25.

Fig. 2 shows fragmentary portions of the rotors, 17 and 18, in their SUCQfiSSive relative positions and providin; the progressive opening and closing of the branch gl des asthey move across respective faces of the branch gl des 1'3 and 14. The motion of the rotors progresses in the directions shown by the arrows with Fig. 2a representing the position of the rotors corresponding to a short interval of time after the instant corresponding to their position in Fig. 1. For this particular device a sine curve was cut backfrom the active edges 21, 21', 22, 22 according to the formula Y=0.38 sin X (inches) a d Where nch a n the X i c e pond d to 1r radians. The inner dimensions of the waveguide were (L4 x 0.9 inch. For these conditions a relative position of slightly less than 100% overlap of the edges 21 and 22, best seen in Fig. 2d; produced optimum results. The sum of the open transmission areas in the branch guides 13, 14 at all positions from a to g during the switching interval remains substantially constant.

The exact character of the relationship between the width of the base of the notch and its depth will depend upon the countour or curve which is used to define the boundary of the notch opening as will be more clearly set forth in relation to Fig. 3. For a given curve chosen for the boundary of the notch, however, an appropriate width-depth ratio can be determined to maintain a substantially constant optim m area of transmission during switching.

These criteria may be used as a first approximation in the design of a transfer switch although, of course, the relative position of the blades may be optimized by slight adjustment after the contours have been cut.

Fig. 3a shows a cut-01f plate 26 positioned across the face of'wave-guide 27 and with a sinusoidal contour 28 providing a progressive barrier in accordance with the electric field intensity variation thereacross. Alternative curves representative of those which the contour could assume to provide a progressive barrier are shown as curve 29 of Fig. 313 and 31 of Fig. 3c. The sense of the curvature in a given case with respect to the straight line of Fig. 3b will dictate a shortened base opening such as that between Points 32 and 32 of Fig. 3a or an extended efiective opening as between points 33 and 33' of Fig. 3c in order to obtain the optimized sum areas of transmission in the branch guides during a switching interval. Although the various contours shown in Fig. 3 provide a marked improvement over prior art devices oi this type, the contour of the type 28 of Fig. 3a or one approximating it such, for example, as a parabola is preferred. This type contour, as utilized in a device s'mlliar to that shown in Fig. 1 to provide switching with an optimized branch guide area balance is the preferred embodiment of this invention for that purpose.

Fig. 4 shows a modification of the present invention similar to Fig. 1 in which a single rotor plate 34 is utilized to control the on and off switching in the two branch guides 35 and 36 and the continuations thereof 35 and 36. This may be accomplished by any convenient configuration of the waveguide which brings the open face of the branch guides into a suitable adjacent position. The contoured notches 37 and 38 are provided in the barrier terminating boundary of the plate 34 as hereinbefore described. The operation of the device of the present invention may be enchanced by the use of choke-to-choke joints 39 and 40 at the open face of the waveguides wherever desired, such joints being old in the art and forming no part of the present invention P H215 Shows the application of the present invention to' a switching operation involving a single waveguide path.

Such applications occnr, for example, when it is desired to intermittently energize and deenergize a load or where it is desired to amplitude modulate a signal to an antenna at an audio rate. Devices used in the past to achieve these results have provided a high standing Wave ratio during the off period and during the switch interval, as well, due to the high reflections which are caused by a straight edged reflecting barrier. Utilizing the teaching of the present invention, a fan-shaped blade 41 is adapted to rotate through a choke joint in a waveguide 42 and the active edges of the blades of the rotor 41 are suitably contoured as at 43. For a device so constructed switching is accomplished with a gradual change in the standing wave ratio in that the highest standing wave ratio does not resultuntil the entire area of the waveguide 42 is covered by the barrier as shown in Fig. 6. Switching accomplished in this manner provides a smaller rate of change of SWR and a lower duty cycle with respect to the existence of higher standing wave ratios thus enhancing the capabilities of the equipment with respect to automatic frequency control, long magnetron life, and the like.

Fig. 7 shows a modification of the principle of this invention as it would be applied in the case of switching a higher order mode of electromagnetic energy. In the case illustrated, rotor 44 has contoured in the active edge 45 thereof two sinusoidal slots 46, 46, which correspond to the electric field distribution of a TE2,0 wave represented symbolically by the arrows 47. By means of this arrangement it can be seen that the'higher order wave energy will be controlled progressively in accordance with the teaching of the present invention;

Obviously other modes of electromagnetic energy or other cross-sectional shaped waveguides could be controlled progressively in accordance with the intensity distribution of the electric field by a suitably contoured barrier element moved in the proper manner and such modifications are within the teaching of the present invention.

What is claimed is:

1'. A rectangular waveguide device comprising a pair of branch guides and a common guide joined to form a common junction, said branch guides having transverse openings therein at multiple quarter-wavelength electrical distances from said junction, a pair of plates movable into wave energy short-eircuiting position in respective ones of said openings and means for moving said plates with respect to said openings to concurrently open-circuit and short-circuit the respective branch guides, said plates leaving and entering said opening along an edge of said guide having variations in the electric field intensity thereacross and the leaving and entering edges of said plates having a contour which varies approximately proportionally as the variation of said intensity across said edge.

2. A rectangular waveguide switching device comprising a common guide and two branch guides joined to form a junction, said branch guides having transverse openings at multiple quarterwavelength electn'cal distances from said junction, a conductive plate movable into wave energy short-circuiting position in each of said openings, said plate entering each of said openings along one of the broad edges of said guide and means for concurrently moving said plate respectively into and out of said short-circuiting position in said branch guides, the leading and trailing edges of said plate extending in substantial parallelism to said one of said broad edges of said respective branch waveguides as said plate moves thereby, and having formed therein generally V-shaped notches conforming approximately to the variation in electric field intensity along the broad dimension of said guide and centered along said broad edge.

3. A device according to claim 2 in which the contour of said notches is approximately sinusoidal.

4. A switching device for a waveguide junction having a pair of branch guides joining a common guide, said device including means coacting with said branch guides for controlling the flow of energy therein, said means comprising a pair of electrically conductive barrier members each movable transversely across a respective one of said branch guides between a position in which said barrier member" completely closes the path of energy flow therethrough and a position in which said path is completely open, means formoving said members in predetermined relation and in opposite senses'to. concurrently close and open said paths of energy flow along respective ones of said branch guides, each of said barrier members having the leading edge thereof so formed that the projection thereof along the axis of the one of said branch guides with which it coacts is concave in the direction of movement of said member, with the most advanced portions thereof moving across the regions of lowest electric field intensity of said branch guide and the trailing edge thereof so formed that the projection thereof along the axis of said branch guide is convex in the direction of movement of said member with the rearmost portions thereof moving across the regions of lowest electrical field intensity of said branch guide.

5. A waveguide switch comprising, a rectangular waveguide having a longer and a shorter cross-sectional dimension, said waveguide being interrupted by a gap extending thereacross, and shutter means movable through said gap for covering and uncovering the full cross-sectional area of said waveguide, said shutter means moving through said gap in a direction substantially parallel to the said shorter dimension thereof, said shutter means having leading and trailing edges formed with notches therein, said notches being substantially centered along said longer dimension as said leading and trailing edges traverse said gap, each of said notches conforming approximately to the variation in electric field intensity along the broad dimension of said waveguide and having an area substantially less than the said cross-sectional area of said waveguide, said waveguide being unrestricted at said gap by means other than said shutter means.

6. In a switch for TEOI energy in a rectangular waveguide having a longer and shorter cross-sectional dimension and having a portion thereof removed to define a transverse interruption with an energy barrier element movable through said interruption across the guide path to control the flow of energy through said waveguide across said interruption, the combination of a predeterminedly contoured barrier terminating boundary for said element, and means for moving said element with said boundary traversing said shorter dimension, said contoured boundary including a recess substantially centered With respect to said longer dimension as it moves in said interruption and said recess having a variation in contour which is approximately proportional to the variation in intensity of the electric field along said longer dimension. 7. A switching device for transferring electromagnetic energy from a common hollow pipe conductor in succession to each of a pair of branch hollow pipe conductors, comprising; means forming a junction between said common and branch conductors, each of said branch conductors having a portion thereof removed to define a transverse interruption, conductive barrier means movable transversely through the interruption of each of said branch conductors from one side thereof to the other to provide a progressive local variation of the cross-sectional opening thereof between a condition in which said opening is completely unobstructed and one in which it is completely closed, the movements of said barrier means being synchronized in a manner such that as the opening in one of said branch conductors is reduced by the move- 6 ment of one of said barrier means the opening in the other is simultaneously increased by a like amount by the movement of the other of said barrier means, the distribution of the electric field intensity across the said openings of said branch conductors being other than a straight line function, the terminating edge of each of said barrier means transverse to the direction of movement thereof being contoured, the contour of each of said terminating edges being a function of the said electric field intensity distribution in the one of said branch conductors across which it moves, in a direction normal to the direction of its movement thereacross.

8. A switching device for transferring electromagnetic energy from a common hollow pipe conductor in succession to each of a pair of branch hollow pipe conductors, comprising means forming a junction between said common and branch conductors, each of said branch conductors having a portion thereof removed to form a transverse interruption, conductive barrier means movable transversely through the interruption of each of said branch waveguides from one side thereof to the other to provide a progressive local variation of the cross-sectional opening thereof between a condition in which said opening is completely unobstructed and one in which it is completely closed, the movements of said barrier means being synchronized in a manner such that as the opening in one of said branch conductors is reduced by the movement of one of said barrier means the opening in the other is simultaneously increased by a like amount by the movement of the other of said barrier means, the distribution of the electric field intensity across the said openings of said branch conductors being other than a straight line function, the terminating edge of each of said barrier means transverse to the direction of movement thereof being contoured, the contour of each of said terminal edges departing from a straight line, extending normally to the direction of its movement across said conductor, by an amount which varies in a proportional relationship to the said intensity distribution along said line of the electric field in said waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 2,206,923 Southworth July 9, 1940 2,415,242 Hershberger Feb. 4, 1947 2,426,992 Folland et a1. Sept. 9, 1947 2,544,715 Muchmore Mar. 13, 1951 OTHER REFERENCES Publication I, Microwave Transmission Circuits, edited by Ragan, vol. 9 of the Radiation Laboratory Series published by McGraw-Hill, May 21, 1948, pp. 522-539. (Copy in Div. 69.)

Publication II, Microwave Duplexers, edited by Smulhn and Montgomery, vol. 14 of the Radiation Laboratory Serres published before April 6, 1948, by McGraw-Hill, page 407. (Copy in Library.) 

